1. Field of the Invention
The present invention relates to a method of producing at least one optical waveguide in the form of a planar structure on a substrate.
2. Background Information
Such methods are known from the article entitled, "Bauelemente der integrierten Optik: eine Einfuhrung," (translation: Integrated Optical Devices: An Introduction), published in the periodical "Laser und Optoelektronik" (translation: Lasers and Optoelectronics), No. 4/1986, pages 323-326. In epitaxial methods, raised optical waveguide structures extending along the surface of the substrate are obtained in that a layer is initially applied to a monocrystalline substrate and is structured photolithographically in the form of the desired optical waveguides, that is, the layer is removed at the locations where the optical waveguide is to be produced. Then an epitaxy method is employed to produce the waveguide as a monocrystalline layer in the form of the structure. Because of the materials to be employed for the substrate, and light waves with substantially coinciding lattice constants which additionally must have different refractive indices, such epitaxial methods are limited at present to a few compounds. The monocrystalline optical waveguides produced by epitaxy generally have a cross section that is approximately adapted to a circular or semicircular shape so that the coupling in or out of light waves at the polished end faces poses relatively few problems.
In diffusion methods one obtains an optical waveguide cross section which is also a close approximation to a circular shape by diffusing doping materials into the substrate, that is, below the substrate surface. The coupling in and out of light waves at the polished end faces here again generally poses no particular problems.
If, however, only a coating method is employed such as, for example, the vapor deposition of a transparent layer and then the structuring of this layer by means of an etching process or by, for example, vapor-depositing a layer through a structured mask, optical waveguides are obtained which have an essentially rectangular cross section that is not well suited for coupling light waves into and out of, for example, an optical fiber.